Valve mechanism for a hydraulic power unit



Jan. 18, 1949. BAKER 2,459,613 VALVE MECHANISM FOR A HYDRAULIC POWER UNIT Filed Feb. 26, 1947 2 Sh e'ets-Sheet 1 [/y VENTOE Gerald 1' Baker x ff 8r I ATT'x Jan. 18, 1949. v G. T. BAKER 2,459,613.

' VALVE MECHANISM FOR A HYDRAULIC fdwEm-IJNIT Filed Feb. 26, 1947 2 sheets-sheet 2 I/vvE/vm/e Gerald T flaker 4 I v 8r A? I I Patented Jan. 18, 1949 UNITED STATES PATENT .O'FFlCEy -j VALVE MECHANISM. FOR A HYDRAULIC POWER UNIT Gerald T. Baker, Neligh, Nebr.

Application February 26, 1947, Serial No. 731,135

3 Claims. (01. 277 53) This invention relates generally to hydraulic power units and in particular to a valve mechanism for a tractor-operated hydraulic power unit adapted to provide for the direct adjustment of a farm implement connected with the power unit or for the direct control of farm implements equipped with separate hydraulic-operated or power cylinders.

A hydraulic power unit now in common use is the John Deere power lift, with which many John Deere tractors are equipped. This lift, particularly the models for the years 1937 through 1946, includes a pair of cranks or lift arms ex tended rearwardly from a tractor and operated by a power cylinder, the supply of fluid to which is controlled through a foot actuated valve mechanism. The lift is generally satisfactory in operation, but some inconvenience in its operation is encountered due to the fact that the valve mechanism, on being actuated, provides forthe movement of the piston in the power cylinder to one or the other of the ends of the power cylinder. As a result, the crank or lift arms, operated from the piston, are moved either to a full up or a full down position. In other'words, the John Deere power lift operates to move and then hold the lift arms at some adjusted position therefor. However, the lift is incapable of mov-' ing the lift arms in a direction opposite to their direction of movement into such adjusted position so that the lift arms must be moved through a full cycle of movements in order to be returned to an initial adjusted position. i

This limitation in the operation of the John Deere lift is particularly objectionable in the lifting and lowering of planter mechanisms, for example, relative to an adjusted planting position therefor, at the ends of rows or to accommodate ground irregularities in a row. Thus the time required to first move the lift arms from an ad'- justed position to a raised position and then through a complete cycle of movements back to their initial adjusted position necessitates that the tractor ordinarily be stopped to avoid a gap or break in the continuity of the planting operation.

Further, when the John Deere power lift is connected to supply fluid under pressure to a power cylinder carried on a farm implement, concurrently or separately-from the supply of fluid-to the power cylinder-in the 1ift,'the same inconvenience is encountered. Thus, for example, in the operation of a hydraulic tractor-mounted loadingattachment, a complete and direct control of the raising and lowering of the loader lifting 2 i arms cannot be attained, since the liftingfarms 1' must be'moved in a continuous direction until they are in one of their extreme positions of op,- eration, before theirmovementcan be "reversed/i It is an object of this invention, therefore, to provide an improved tractor-operated hydraulicf power unit. A I I Another object of this invention is to providea'n improved valve mechanism fora tractor-operated hydraulic power unit.

A further object of thisinventionis to provide a valve mechanism for a hydraulic power lift" which is capable of controlling the supply of fluid to, or its release from, a power cyli'nclerat any moved position of the piston for su'chcylinder".

Another object of this invention is to provide avalve mechanism for a tractor-operated hydraulic power lift, which is adapted to control the operation of a power cylinder to accomplish a complete overall maneuverability of a lift member, oper'-" atively associated with a cylinder, with amin'iv mum of effort and attention. I

A still further objectof this invention is to provide a valve mechanism for a tractor-operated hydraulic power unit for a tractor, which is adapted to immediately provide for the direct 'adjustment 'of a lift member to any moved position f therefor, so as to eliminate the'lift member being moved through a predetermined cycle ofmovements to an adjusted 'position.

[Yet 'anotherobject of this invention is to provide a valve mechanism for controlling the"s'up-' ply of'fluid to the power cylinder'of a hydraulic unit, which is of a compact and economical con' struction, capable of providing for the direct movement of the piston for the power cylinder from one position to any other movedposltion therefor, and adapted to be either foot or hand actuated.

Further objects, features and advantages of this invention will appear from the following description when taken in connection with theI-accompanying drawings, in which: Fig. 1 is a longitudinal sectional view of 'a John Deere power lift with a pump unit illustrated diagrammatically and showing the valve mechar'v cam pockets L, H and R, with the pocket H being arranged intermediate the pockets L and R.

The bypass valve 3? comprises a valve member 48 of a cylindrical tubular form, having a closed upper end 49. Annular grooves 50 and 5i, arranged adjacent to bottom and top ends, respectively, of the valve member 48, are provided with a series of holes or openings 55 and 52, respectively,.which arev open to the interior of the valve member 18. j t

The valve member 48 (Fig. 1) is slidably supported in a bore 53 formed in a portion 54 of the Fig. 8 is a fragmentary sectional detail" view" showing the application of the power unit 'fbr' operating a separate or independent-hydraulic.

cylinder.

With reference to the drawings;'tlie valvemechanism of this invention is illustrated in: Figs: 1' and 2, in assembly relation with a John Deere hydraulic power lift, which includes a housing, designatedigenerally as 1D,. integrally formed. with a motor orpower cylinder tl an oilreservoir 1.2, a bypassor highpressure.oil.passage l.3-connect'ed betwee'n the reservoir. 1 2 and a pump unit [4, .and a .motor oil-passage ll6',. of! an. irregularshape, connected with the power cylinder I l and with thepassage l3 through- 21, fluid-opening or motor port. 2 0 formed in. a partition wall 25i constructedas part of the housing 10. Theterminal end of the. high pressure fluid. passage I 3 isrdefined byta fluid discharge portifiyA piston. 11, for. the

cylinderhas a connecting rod 18, whichis pivoted.v at- :l 9- wlth a. crank arm It for. a crank shaftrlz, which. carries as-pain; of..lift j arms (not. shown) .arrangedto. the outside and on. opposite sides of thehousing HLMWhen. the-power lift is mounted on a tractor. theLlif-tarms are extended. rearwandly fromtthe. tractor rear axle for pivotal= upand downv movement. For. the. purpose of conveniencein description, the .cylinderend. of the housing willbe referredto-as its frontend.

Assembled within the. housing. Ill-is a camshaft 23,. having-a rock amn- ZA-locatedoutside ofbthe.

housing; rm, and, connected througha pivotedlink. 26 with-a foot: pedalnzl mounted: on a f ootactu ated shaft 28,,which is rotatably= supported-- in bearingsiaarrangedi in. a spaced relation on. thetop-of-the housing J0. Inrausual. assembly the foot pedal is arrangedbelow: the tractor operator's-seats A- shaft/-37! ,.rota tably supported imthe housing, [0 inJ-a. spaced parallel relation with the: 'cam shaft. -23; but. below and" grearwardlyof. thershait z carries am-arm- 32s, the-free or'upper endeot which is acted upon by a compression spring 88, to: continuously bias the shaft--34- in. ascounter-clockwise direction; as viewed ineFig;v 1=. A secontiiamn' fl mountedzom theshaftiti carriesa cam roller 36 for a purpose which will :appear later; r

The structure ahusfar "described formsrno part ofthe present invention and is part of a commercially available t-ype of a John-Deerepower-- liftfi- Thexvalve meehanismef this invention (mg;v 6') includes a bypass' valve'l'l; a check valve 38; :and a 'cami unit 39a. "lithe unit Mr-is an integral: casting: formed with a hub or: sleeve 'memberl l adapted? to b'e mounted: on the: camshaft as. A

split portion 12 at onc:errd ofrthe hubill', canties a clamping. bolth for securingrthe: huh Me on the shaft 23. Spaced axially on the hub 4l,,ianfil order from the splitpomon flg are a lug: ill, a selector cam 46, and anactuaflngrcam: i Tha selectorcam: 18- is=formedi with indentatibnsor housing l0, which portion also includes a part of the" passage i3; and is arranged for up and down movement transversely across the outlet end or discharge port 56 of the passage [3 at a position such that its longitudinal axis lies in a plane common to" the axis for the cam shaft The cam 44 is arranged relative to the valve member 48 so that its outer peripheral surface is adapted for hearing engagement Withthe closed'end 49 of the valve member. This bearing engagement is yieldably maintained'by the 'provision of' a coil'sprlng 57 positioned withinthe" valve member 48' and arranged injcompression between its closed end 49and an upright bearing" portion iflformed'a's part of the housing IU The check valve 38 (Figs. 4, 6 and?) includes" a valve stem 59 formed with a reduced section 6! at its lower end ..'as viewed in Fig. 7. "A'

threaded. extension 62 projects axially down wardly from. the reduced section SI for connection. with a cap nut or valve member 63', which has one end- 611 threadable on the shanlg'fifand'l an. annular cavity 56 formed in its opposite end in coaxial alignment with thethreaded extension" 62. The end Bl, ofthe cap or \valvemember 63,

is ofa greater diameter than the reduced section 6| of'the valve stem 59'; and is adapted for abutting engagement withthe shoulder 61 which defines: the junction of the extension 52 with the section 6]..

A valve seat. 65 (Fig. 7) on the inner or top end 54- of the cap v63' is adapted for. seating engagement with. a matingvalve seat lis'formed' at thedower end-of; a valve member 69,- which is; axially movable, on the .reduced sectionflii betweenthe valve. seat. 5ft and the shoulder H which defines the upper end ofv the reduced sec tion BL: The. center. bore '12 ofthe valve meme be}? 6Q-is ofagreater diameter than the reduced section 6| so that a. space. or clearance 'iTjis provided. 'therebetween.

A- second: valveseat. 13,. on the valve member 69;. isadapted forseating engagement with a valve seat 1*. (Fig. 4-) formed in the partition" wall- -25 and about the lower. end. of the. motor port or. opening: 20,.which is incoaxialaligmnent with the bore 53-=for the valve member 48. The

opposite sides-of the valve seat '13 arefluid-connected. by downwardly and inwardly inclined passages '16 (Fig. 7 formedin the valve-memeber 69- with' their inner ends open to the space H- between the bore 1:2 andthereduced section ilhe valve" stem 59- (Fig. 4'.) extends upwardly through-the opening 20, which constitutes the jumitioniof the. passages: 13 and: I6, andthrough, 7 an: opening: irrthe bearing '58,, so as to project. within thecoil; spring 5'? for thevalve member; 48 to: a position adjacent to-the closed end 49 of. the :valvemember: 48*. This assembly isv ac complished: on! removal of the drainplug 18 7 6i carriedl in; the: housing 10-. at. the bottom ofthe;

' tor cam 46;

In the operation of the valve mechanism;'

5 oil 'pa'ssage' I6. The seat" on the valve memher 69 is yieldably maintained orurged into a closing "relation with the-valve seat 14" by a'compression spring 19 havin its upper end seated irithe cavity 66 of 'the 'capmember63, and its lower end in abutting engagement with the plug assum'ethepiston l1 andthe valve mechanism to be in their relative positions, illustrated .in Fig." 1,'-representing a' moved position of the piston providing for an adjustedposition of the lift arms associated with the crank shaft 22, anda position for the valve mechanism which will hereinafter be referred to as its hold position In this hold position the valve seats I3 and 14, and the valve seats 65 and 68 are in their" closed positions so that no flow of oil takes place between the passages 13 and i6; -As' a result any -'oil in the passage l6 and the'cylinder H is-trapped therein'and the piston l'l is'held by "such trapped fluid against forward movement toward its top center position. The'check valve 38 is thus closed when the valve mechanism is in a'hold position.

With the check valve 38 closed, the lower peripheral groove 5ll,inth'e valve member 48,"partially extends within the outlet end 56 of the passage l3 whereby. oil from the passage I3 is permitted to'flow through the openings 55' into the "valve member 48, and outwardly from the valve member and into the oil reservoir "through the openings 52 in the topperipheral groove 5i which is positioned at all times above the housing portion 54. It is-thus seen that the bore 'It'is seen, therefore, that the check valve 38,"

iii

or space within the by-pass valve member 48 constitutes a fluid passage with the openings" 55' defining its inlet, and the openings 52 and-open lower end of the member 48, the outlets'therefor. Oildischarge from the" pump 14 into the passage I3 -thus "bypasses the passage l6 forflow through the open bypass valve 37 into the reservoir l2, and from the reservoir 12 through a-pa'ssage 8| to the inlet of the pump l4.;' This complementary action of the check valve38 and bypass valve 3'! is maintained byjthe cam, which on being actuated to the hold position for the valve mechanism, provides for an upward movement-of the valve member 48 suchthatf-its closed end 49 is out of engagement with the upper end 82 of the valve stem'59 (Fig. 1).

The rotation of the actuating cam 44 to pro vide--fora hold position of the valve mechanism is' accomplished by rotation of the selector cam 46, in response to the movement of the foot pedal Z'ltoaposition determined by the reception'of the cam roller 36 within the cam pocket H,"or* neutral position onthe'selector cam 46'. The' reception of the roller 36 in one of'th'e cam pockets L, Hxand R is'evidenced by the feel on-the foot pedal.

In order to raise the lifting mate-5,. as

" a cutaway'porti'on to provide a shoulder 99 for sociated with the'crank shaft 22, fluid under pressure 'is supplied to thecylinder II to move the piston l1 rearwardly from its position shown in Fig. 1- to its position-shown in Fig. 3, wherebythe crank shaft 22 is rotated in a clockwise direction,'as viewed in Fig. 3. This is accomplished by tilting the foot pedal 21 in a rearward direction, from'its position shown in Fig, 1 'to its position shown inFig. 3', so as to depress the link 26. To facilitate this movement of the foot pedal 21, there is provided a hand operated lever 83 which is secured, by means including a. bracket 84, to the foot pedal 21 at a position forwardlyof its pivotal support in the bearings '29; ;j

The rearward tilting movement of the foo pedal 21 through the link connection 26-, rotates The. reception of the roller 36' within the camv pocket R defines the raise position'of the valve mechanism. l

The actuating cam 44, on rotation from a hold position to its raise position, releases the valve member 48 for upward movement by the spring,

51 to a position such that the peripheral groove 50 is moved out of fluidcommunication with the? passage l3, to provide for the passage being closed: at its outlet end 56 by the lower end portion 86;-

of the valve member 48.

As a result, an oil pressure is built up in the. passage l3 which is capable of opening the valve" member 69 against the pressure of the spring 19,

so'that oil from the passage 13' flows through the opening 20 and into the passage 66 to the cylinder l l.- Fluid under pressure will thus be supplied tothe cylinder H until the foot pedal 21 is tilted forwardly to its hold position shown in Fig. 1.

To accomplish an automatic movement of the camunit 39 to its hold position, concurrently with the movement of the piston IT to its rearmost or bottom center position therefor, which defines a maximum lifting action of the power unit, there is provided a limit device, indicated generally at 81in Figs. 2, 5 and 6.

The limit device includes a bell crank which is mounted on the shaft 3i with an upper arm 88 extended upwardly to a position above the shaft 23, and a lower arm 89 projected downwardly to a position at substantiall the level of the longitudinal axis of the cylinder II.

The free end of the lower arm 89 is in bearing engagement with the rear end of a pin 9i extend ed longitudinally of the cylinder H and slidably supported in an upright projection 92 formed in the housing ID. The forward movement of the' slidable' pin 9| toward-the cylinder Ii is limited by the engagementof'a cotter key '93, extended therethrough, with the rear side of the projer housing I 0.

Pivotally connected at 91 with the free end .of the-upper arm 86 is a pawl member 98 which extendsin a forward direction across the top of the cam unit sleeve 4| at a position between the selector cam 46 and the split end portion 42. The" pawl 98 is formed at its free or'forward end with amines tion, illustrated at B in Fig. 5, the pin 9| is moved reanwardly against: the action ofthe: spring 94, whereby the arms 88 and. 89. are pivoted in a clockwise direction; asviewed in Fig. 5. This movement of the arms 88 and 89 in'turn moves the-*pawlllih in aforward direction to engage theshoulder. BQIWiththe-lugdlso as the piston moves to its rear position, shown in dotted lines at B inuFig: 53 The cam unit 39 .is then rotated: in a clockwise direction to aposition pi'ovidingzior the roller=36ibeing received inthe neutral portion H of the selector cam 45. At this position; or the cam unit 3.9; the bypass valve: and; checle valve 38- are actuated to their. hold positions indicated. air-Fig. 11'It is to benoted. for a purpose-which: Will -appear. later; that the: shoulder; 9.92 is moved forwardly out-of engagement-with thelug-Mh so that the: bottom side of. the l pawl-98 rests on: the lug 40. i

To release the fluid pressure applied: 011517118 piston I 1," topermit a. rotation. of the crank shaft it' in: a counter-clockwise direction", to; inturn: provide for a lowering ofthefliftrmembers.assoe ciateditherewith; the. foot: pedali21: is; tilted. f or-- wardly. from its position shown imFig: 1- to=its positionshown'in Fig; 4-. This movement, of; the: foot: pedal "2 1; throughthe link 2 6; and rocker-arm: 24, rotates the cam unit 39: in. awclockwise direc tion: from" its positionshown in .Fig. 11'. .to-its positiomshown in Fig. 4, to providefor. the reception of the cam. roller 36 inthepoeket Let the se:-- lector cam. 46, which defines the releasezor low.-- ering-nositionof the valve mechanism.

During; therotation of the cam-;unit. 3.9: from a hold position to-arelease position, .the-actuating- .cam .moves-the valve member48oi thebypass valve- 31 in a downward direction. to a po-- sition at whichthe peripheral groove :50, is open. toithe fluidpassage I3,- wherebyfluid-from the: passage I3; is permitted to flow into thez-reser..- voir I2. Concurrently with this aotuationmf-the: bypassvalve 3-1; the closed endi49z of. the"; valve member. 48 engages and. moves,- the rvalvestem; 5% downwardly against the actionofzthe-springflaso;as-to=open the check valve 38. Fluid fromihecylinder II isthus permitted to flow intothe' passage I5, and: outwardly: therefrom into; the.

passage I3 for returnz-to-thereservoir 25. l

Itis. seemtherefore; that thervalve'meoh-anism is directlyyresponsive-in operationtoamactuatiom oithe-ioot pedal 2-? te-provide?foraimovement.

position therefor,- and to hold the piston;- I against movement at any moved position:

Ifit is; desireditoislowly lower the. liftingmemhers;associatedwith-the crankishaft 2.2; thegfoot pedal; 21; from its position. ShOWIhin1E1g-; 1', ir2 only tipped slightly forwardithrough adistanoez sufiioient' to provide fora downward. movementof. the=valveistemz591by'the. closedend; 49 of the:

valveemem'ber' 4-8, to; nrovideiqr-the:enga ement; ui-nectionu-flfiiand cylinder I02.

saizpedahfl; to; its raise. positioni Since the. pistoni' ofzgthershoulder 11 withzthetupperrendi of.

member lindEllg 'lyfi At-, this..;move.dposition of the; valve stemrelative to;th e-.--va1ve. member 6.9; the'ivalveaseati 65.: on the 5.039211181111361 53 .is 3011i 01' engagementi With:- the] valve .seat 68 on'the l valve member wills whereby fluid is permitted to flow from the pass,

sage :Ifigjinto, the space" andzoutwardlythemfrom-throu hithe'passages.1fiwinto=the oil passage; I 3; The check. valves3-8, by "virtue of: thisractiom. isythuseonlycracked to permit? a. slow flowvofithafluidafrom. the passage: I 6 into the passage:- 1 L for. travel into the reservoir I24.

wolincreasetheflowof oil=from:the:cylinder:-I'I into: therpassage I3; thefootpedal 21.- may; be: progressively moved toward itsposition showm in;1l'ig;; :4until.a -.max-imum opening of the check. valyei3flz is obtained: I v

Inf. those instances: where: agseparate hydraulic. cylinder, associated with a farm implemennistm:

be"; operated: independently: of; the, liftl members assooiatediwithi the a crank shaft.- 2'2 the: plug;- 51!.

isaremoved and anlirconnection- I05 or the likei (Fig. 8).,may he-substituted therefor-.- 'Awcyllnder Inrwhich; ;for-example; may-formapantzofia trace" 7 tor: 'loaden attachment, isrthen suitably-connected: with-the connection. H15; The spring! 1910f; the: check valve 38 then bears; directlwagainst the: inner; end of the connection I055 as: shownyinr Fig. 8:

limit device 8-1-will take placeiprior tonanymove-f mentsortherpiston Iflfizfor the cylinder: I I12. How.- ever, as: illustrated: in: dotted lines: Fig; 5;;the shouldenEI-B onithe:pawl .9 8v, atra rearmostipositiom for:- thepiston! I-1 is -:out of? engagement :with a the lug; 40;; Inother 'words the shoulder 9-9sis-;mdvedi forwardlyout: of engagement with: the" lug: 4m.-

after: the: selector cam 48: has; been *moved: to 2-! position to locate-the roller 36: within: the cam .pooketI-I; r

returnedwby. the action of.- the limitv device 81;, from itssraise position. in Fig.- 3 to'itshold position. intFig; -1,.it.. is only necessaryto agaimmoveitha:

I 1: is. in its rearmostpositiom this; second.- moyementr-of I the pedal 2.1to,its=raise.position iniEig. .3, takes place because. the lug. 4min the: cam-. units 3% is capable of slidably engaging the under aside-1' ot. therpawl. 98 to. merely: pivot the pawl: in: an

upward-direction.

The paw1.9.8., after. the. piston. I 1 zhasibeenzmovedi toiitsi-rearmost. position is thusrenderediinonr' erative so that*onlatertactuation of the pedal 21.

fiivs'the valveimech-anism' is; operated; in all respects OfithQ'DiStOIll I1 ineither directioniiromaa moviedz' similar to.its .oper-ation' relative; to the -contr0l.:of

the.- crank shaft 22,- to. control: the operation of; the piston; I 03-of -.the-cylinder l0,2., Stated other=i wisepaitenthe; piston. I .1'has .beenimovedtorit'sfl myrearmos-t.positionithes cylinder II and'za portion; of the passage. I6; merely -c.onstitute:.an'.oi1 resera voirrandxtha valve:- mechanism.- controls; thesaflow' of; oil throughrthexpassage; I3; .a 1 part? of the-ar as?v sage l6, and through the check valve 38, cans- .Invsupplyingsfluidt underrpressure-rto 'theicyline movement;ofithe'piston 1:15 and operation ofs' the -As-jasresult, when thefoot pedal 21! has-been? Further, due to the operation of the limit device 8'! being rendered ineffective by the initial actuation of the pedal 21 to a raise position, the raising and lowering of the piston I03, and its retention in a moved position, takes place entirely in response to the operation of the foot pedal Z'l. It is apparent also that a double operation of the pedal 27 to a raise position is necessary for only the initial lifting of the piston 103, and that any later raising of the piston I03 will take place in direct response to a movement of the pedal 21 to its raise position.

From a consideration of the above description, it is seen that the valve mechanism of this invention is readily applicable to a commercially available power liit, to provide for a complete and direct adjustment of lift members associated with the power unit, to any desired adjusted position without requiring the movement of the lift members through a predetermined cycle of movement. Further, the valve mechanism operates efliciently to accomplish a direct movement of a lift piston, associated with a lift cylinder separate from the power unit but in fluid connection therewith, so that the unit is capable of use with hydraulicallyoperated farm implements which are attachable to the tractor.

Although the invention has been described with respect to a preferred embodiment thereof, it is to be understood that it is not to be so limited since changes can be made therein which are within the full intended scope of this invention, as defined by the appended claims.

I claim:

1. A valve mechanism for a hydraulic power unit including a casing formed with a high pressure fluid passage having a fluid discharge port at its terminal end and a fluid port intermediate its ends, said mechanism including a by-pass valve member co-aXial with said intermediate port and reciprocally movable relative to said discharge port to control the flow of high pressure fluid through said discharge port, said by-pass valve being formed with a fluid passage therein having a fluid outlet opening and a fluid inlet opening which is movable into and out of registration with said fluid discharge port, a check valve for controlling the flow of fluid through said intermediate port, means for yieldably holding said check valve in a closed position therefor, and means for operating said check valve and by-pass valve in a complementary relation such that said check valve is opened by said operating means, when said by-pass valve is moved to a first position in which said fluid inlet opening is in registration with said fluid discharge port, and by the pressure of the fluid in said high pressure fluid passage when said by-pass valve is moved to a second position in which said fluid inlet opening is out of registration with said fluid discharge port, with said check valve being closed by said yieldable means on movement of said by-pass valve to a third position, intermediate said first and second positions therefor, in which third position said fluid inlet opening is in partial registration with said discharge port.

2. A valve mechanism for a hydraulic power unit including a casing formed with a high pressure fluid passage having a fluid discharge port at its terminal end and a fluid port intermediate its ends, said mechanism including a reciprocatmg by-pass valve for controlling the flow of fluid through said discharge port arranged in a coaxial relation with said intermediate port, a check valve for controlling the flow of fluid through said motor port having a stem member engageable by said 'by-pass valve, a first valve member mounted in a spaced relation about said stem member for movement axially thereof, a seat portion on said first valve member adapted for seating engagement with a seat portion formed about said intermediate port, said first valve member having fluid passages formed therein within the confines of said seat portion thereon to fluid connect said intermediate port with the space between said stem member and said first valve member, a stop portion on said stem member for limiting the movement of said first valve member toward said by-pass valve, a second valve member on said stem member formed with a seat portion engageable with said first valve member to close one end of the space formed between said stem and flrst valve member, said second valve member constituting a stop for limiting the movement of said first valve member away from said bypass valve, yieldable means acting on said second valve member to maintain said two valve members in a seated relation, and said first valve member seated relative to said intermediate port, and means for reciprocating said by-pass Valve to relatively control the flow of fluid through said discharge and intermediate ports, said by-pass valve on movement thereof to engage and move said valve stem, providing for the opening of said second valve member prior to any opening movement of said first valvemember.

3. A valve mechanism for a hydraulic power unit including a casing formed with a high pressure fluid passage having a fluid discharge port at its terminal end and a fluid port intermediate its ends, said mechanism including a reciprocally movable by-pass valve for controlling the'flow of fluid through said discharge port, a check valve for controlling the flow of fluid through said intermediate port arranged in coaxial alignment with said by-pass valve, said check valve including a pair of cooperating valve members relatively arranged and constructed to close said intermediate port, with one of said valve members adapted to be opened relative to the second one of said valve members to partially open said intermediate port, means acting on said one valve member to yieldably maintain said two valve members in closed positions, and means on said check valve engageable with said by-pass valve, on movement of said by-pass valve in one direction to open said discharge port, such that said one valve member is opened prior to any opening movement of said second valve member.

GERALD T. BAKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

